Chirality and the associated optical activity is an important property of many organic and biological compounds. A molecule that can exist as two mirror images which are not superimposable on each other are called chiral. Although molecular chirality has been known for a long time, chiral conducting polymers have only recently been reported. Some chiral conducting polymers, such as chiral polythiophene (Salmon et al, J. Electrochem. Soc., 132, 1897 (1985)), chiral polypyrrole with an amino acid substituted on the 3-position (Kotkar et al, J. Chem. Soc. Chem. Commen., 917 (1988)), and electrochemically polymerized chiral N-substituted polypyrrole (Delabouglise et al, Synth. Met., 39, 117 (1990)), have been described in the art. Chiral polyaniline has been synthesized by the electropolymerization of aniline in the presence of D-camphor sulfonic acid, as described by Majidi et al, Polymer, 35, 3113 (1994), and has been synthesized by doping a polyaniline emeraldine base with D- or L-camphor sulfonic acid, as described by Majidi et al, Polymer, 36, 3597 (1995).
Polyaniline is the name given to the polymer having the structure, in a completely reduced leucoemeraldine oxidation state, of the general formula: ##STR1## where n is greater than about 25 and where R is a hydrogen atom. Alternatively, R may be a substituent, such as, for example, an organic group, including, for example, CH.sub.3, C.sub.2 H.sub.5, OCH.sub.3, N(CH.sub.3).sub.2, an inorganic group, including, for example, F, Cl, Br, I, or a metal chelate group. For all the polyanilines described herein, the appropriate choice of an R group permits a greater range of solubility in a greater number of different types of solvents, which results in increased versatility for processing the polymers and a greater range of chemical properties.
Polyanilines can, in principle, exist in other oxidation states. Masters et al, Syn. Met., 41-43, 715 (1991). For example, polyanilines can exist in the completely oxidized pernigraniline oxidation sate of the general formula: ##STR2## where n is greater than about 25 and where R is a hydrogen atom or a substituent, such as, for example, an organic group, including, for example, CH.sub.3, C.sub.2 H.sub.5, OCH.sub.3, N(CH.sub.3).sub.2, an inorganic group, including, for example, F, Cl, Br, I, or a metal chelate group. Polyanilines can also exist in the partially oxidized emeraldine oxidation state of the general formula: ##STR3## where n is greater than about 25 and where R is a hydrogen atom or a substituent, such as, for example, an organic group, including, for example, CH.sub.3, C.sub.2 H.sub.5, OCH.sub.3, N(CH.sub.3).sub.2, an inorganic group, including, for example, F, Cl, Br, I, or a metal chelate group. The emeraldine oxidation state can be protonated by protonic acids, e.g., HA, to give polymers of the general formula: ##STR4## where n is greater than about 25 and where R is a hydrogen atom or a substituent, such as, for example, an organic group, including, for example, CH.sub.3, C.sub.2 H.sub.5, OCH.sub.3, N(CH.sub.3).sub.2, an inorganic group, including, for example, F, Cl, Br, I, or a metal chelate group, which exhibit a significant increase in electrical conductivity.
It is well known that the chirality of a molecule induces optical activity. Generally, there are several methods which can be used to characterize the optical activity of a molecule, including optical rotatory dispersion (ORD), circular dichroism (CD) and optical rotation ([.alpha.].sub.D). Of these, circular dichroism is the most powerful and sensitive method for the measurement of the chiroptical properties of chiral molecules. For example, electrochemically synthesized chiral polyaniline, as described by Majidi et al, supra, exhibits CD absorption in the UV/Vis region at about 300 nm to 800 nm.
Because chiral conducting polymers offer the unique combination of electronic properties and the character of molecular recognition, there are many important applications for chiral conducting polymers. For example, chiral polymers can be used as chiral electrodes for asymmetric synthesis, as biological sensors, and as chiral separation materials in pharmaceutical applications.
Since previous studies have only focused on the electrochemical polymerization of chiral monomers, there is a need in the art for, among other things, novel methods of chemically synthesizing chiral polyanilines.